Re: [PATCH v2 0/4] nbd/server: Quiesce coroutines on context switch

[Sergio Lopez <slp@redhat.com>]

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On Wed, Jan 20, 2021 at 02:49:14PM -0600, Eric Blake wrote:
> On 12/14/20 11:05 AM, Sergio Lopez wrote:
> > This series allows the NBD server to properly switch between AIO contexts,
> > having quiesced recv_coroutine and send_coroutine before doing the transition.
> > 
> > We need this because we send back devices running in IO Thread owned contexts
> > to the main context when stopping the data plane, something that can happen
> > multiple times during the lifetime of a VM (usually during the boot sequence or
> > on a reboot), and we drag the NBD server of the correspoing export with it.
> > 
> > While there, fix also a problem caused by a cross-dependency between
> > closing the export's client connections and draining the block
> > layer. The visible effect of this problem was QEMU getting hung when
> > the guest request a power off while there's an active NBD client.
> > 
> > v2:
> >  - Replace "virtio-blk: Acquire context while switching them on
> >  dataplane start" with "block: Honor blk_set_aio_context() context
> >  requirements" (Kevin Wolf)
> >  - Add "block: Avoid processing BDS twice in
> >  bdrv_set_aio_context_ignore()"
> >  - Add "block: Close block exports in two steps"
> >  - Rename nbd_read_eof() to nbd_server_read_eof() (Eric Blake)
> >  - Fix double space and typo in comment. (Eric Blake)
> 
> ping - where do we stand on this series?  Patches 1 and 3 have positive
> reviews, I'll queue them now; patches 2 and 4 had enough comments that
> I'm guessing I should wait for a v3?

Yes, I have almost ready a v3. Will send it out today. I think it'd be
better to pull all four patches at the same time, as "block: Honor
blk_set_aio_context() context requirements" may cause trouble without
the patch to avoid double processing in
"bdrv_set_aio_context_ignore()".

Thanks,
Sergio.
 
> > 
> > Sergio Lopez (4):
> >   block: Honor blk_set_aio_context() context requirements
> >   block: Avoid processing BDS twice in bdrv_set_aio_context_ignore()
> >   nbd/server: Quiesce coroutines on context switch
> >   block: Close block exports in two steps
> > 
> >  block.c                         |  27 ++++++-
> >  block/export/export.c           |  10 +--
> >  blockdev-nbd.c                  |   2 +-
> >  hw/block/dataplane/virtio-blk.c |   4 ++
> >  hw/block/dataplane/xen-block.c  |   7 +-
> >  hw/scsi/virtio-scsi.c           |   6 +-
> >  include/block/export.h          |   4 +-
> >  nbd/server.c                    | 120 ++++++++++++++++++++++++++++----
> >  qemu-nbd.c                      |   2 +-
> >  stubs/blk-exp-close-all.c       |   2 +-
> >  10 files changed, 156 insertions(+), 28 deletions(-)
> > 
> 
> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3226
> Virtualization:  qemu.org | libvirt.org
> 

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